With today's more complex networks ranging from corporate intranets and extranets to the Internet itself, there is tremendous pressure from telecom service providers as well as end customers to establish fully defined and measurable levels of service that can be directly affiliated with users or user groups. Most corporate intranets and metropolitan networks are built with the familiar IP routing protocol. IP, which transmits packets asynchronously, is a connectionless protocol that provides no guarantees about the timeliness or relative order of the packets. It is difficult to identify traffic congestion and network delays caused by malfunctioning network hardware. Telecom transmission links are inherently constrained by bandwidth. If packets are placed into the transmission queue faster than they are actually transported, packets usually will be delayed and some might eventually be dropped. It is difficult for carriers and ISPs to quantify these discarded packets and determine what are acceptable packet transmission delay thresholds on a per-customer basis.
Many high profile telecom service customers such as investment banks and government agencies are thirsting for definitive service level guarantees so that the appropriate telecom service level can be purchased for the transport of various types of mission-critical information.
The questions of how often can network packets be lost before the network service becomes useless, and how much delay is too long are some of the questions that telecom service users are asking the service carriers in an attempt to shore up definitive service guarantees and hold the carriers liable should the service agreements be violated. These questions do not have inherently right or wrong answers. If a network carrying mostly e-mail is out of service for an hour, some might not even notice. But for a system performing credit card validations, being out of service for an hour at a retail store could cause consumer protests. All networks have varying service qualities from time to time as traffic comes and goes. This is where the idea of Service Level Agreements (SLA) enters. SLAs are essentially promises on the part of the network service provider to each major user group that the level of service provided by the network will be within the bounds established by the SLAs. While 100% uptime may be every telecom service users' goal, 99% to 99.999% are more realistic averages. One key element of network SLAs is to stipulate the penalties for downtime during critical business hours. For instance, downtime at 2 a.m. may not disrupt the typical enterprise's business, but it could be unsatisfactory for an e-commerce application. Typically, compensation takes the form of service fee refund or free service for a pre-agreed upon number of days. Another key part of guaranteeing network service is the connection SLA, which basically means acceptable data losses and data latency (or data delays). According to a recent study by the telecommunications industry, it was found that a very small number of service providers actually detailed provisions for data loss (which results from data packets being dropped in congested networks) and data latency in their SLAs. To illustrate the range of acceptable data loss rates, one has to understand that for real-time applications such as Voice over IP, a data loss rate of 1% could prevent the application from operating effectively. On the other hand, a packet loss rate in the 5 percent range is quite acceptable for typical Internet browsing. Network SLAs are specified and quantified by the Quality of Service that an individual service customer can purchase. The QoS architecture is considered vital in maximizing network utilization while providing diverse service guarantees.
The underlying network hardware and software responsible for “policing” and allocating the appropriate resources for the Service Level Agreements should supplement the existing collection of Operations, Administration, Maintenance and Protection services currently in place on each network element for providing network metrics. In other words, the infrastructure needed for SLA implementation typically resides on the network element itself or some portion thereof.
Even though some current network equipment undergoes strenuous seismic, weather and extreme thermal tests to assure the high reliability of the hardware components which translates into network uptimes as high as 99.999% during the operational life of the network equipment, these hardware tests could not reveal real-time network delay as well as the packet drop counts (thus no method of formulating connection SLAs) during periods of network congestion. It would be advantageous to have an effective way of accurately determining transmission delay and packet drop data on a per-customer basis. The ability to define connection SLAs based on concrete data would give these telecom carriers a competitive advantage because it clearly delineates the type of service that an individual customer should be expecting.